1. Field of the Invention
The present invention relates to a rotation detecting apparatus provided for detecting a rotational angle of a steering wheel of an automobile or the like and a method of fabricating the same.
2. Description of Related Art
There is a conventional rotation detecting apparatus described in, for example, JP-A-2000-283705 as shown by FIG. 8. FIG. 8A is a sectional view of an essential portion thereof and FIG. 8B is a sectional view of a driven gear detached of a magnet. FIG. 8A shows a rotation detecting apparatus integrated to a rotational connector apparatus 101 for electrically connecting a vehicle body side thereof and a steering wheel side thereof.
A rotation detecting apparatus 107 is provided between a lower housing member 103 and a lower cover member 105 of the rotational connector apparatus 101. The rotation detecting apparatus 107 is generally constituted by a drive gear 109, a driven gear 111, and a circuit board 113.
The drive gear 109 is constructed by a constitution of being cooperatively rotated in accordance with rotation of the steering wheel. The driven gear 111 is brought in mesh with the drive gear 109. The driven gear 111 is provided with a magnet 115 at a rotational center portion thereof. The magnet 115 includes a plane portion 117. The plane portion 117 is contiguously formed with an N pole and an S pole with a rotational center of the driven gear 111 as a boundary. The driven gear 111 is constructed by a constitution in which one face side thereof is rotatably supported by the cover member 105 and other face side thereof is brought into sliding contact with the circuit board 113. The circuit board 113 is provided with a magnetic reluctance element 119 opposed to the plane portion 117 of the magnet 115.
A portion of the driven gear 111 for attaching the magnet 115 is as shown by FIG. 8B. The driven gear 111 is provided with a holding hole 123 for holding the magnet 115. An inner peripheral wall of the holding hole 123 is provided with a stepped portion 125 and a plurality of press claw members 127 are provided along the inner peripheral wall in a peripheral direction at predetermined intervals. A front end of the press claw member 127 is provided with a press claw 129.
The magnet 115 is contained at inside of the holding hole 123 while opening the press claw members 127 and the stepped portion 125 and the press claws 129 are engaged with the magnet 115 by closing the press claw members 127 to thereby attach the magnet 115.
Further, when the drive gear 109 is rotated in accordance with steering of the steering wheel, the driven gear 111 is rotated cooperatively therewith. When the magnet 115 is rotated by rotating the driven gear 111, a magnetic field of the magnetic reluctance element 119 opposed to the plane portion 117 formed with the N pole and the S pole is changed and a reluctance value of the magnetic reluctance element 119 is changed in accordance with the change. An angle signal can be outputted to an external system by converting the change into the angle signal by an electronic circuit portion.
Therefore, a steering angle of the steering wheel or the like can accurately be detected without restricting an angle detecting range.
Meanwhile, a direction of integrating the magnet 115 is restricted to make the plane portion 117 contiguously formed with the N pole and the S pole opposed to the magnetic reluctance element 119. Therefore, when the magnet 115 is formed by injection molding, the plane portion 117 needs to firmly be opposed to the magnetic reluctance element 119 by determining the plane portion 117 formed with the N pole and the S pole based on identification of a so-to-speak gate mark or the like and the integration becomes significantly troublesome.
Further, there is a concern of deteriorating detection accuracy by introducing an error in detecting rotation by shifting a rotational center of the driven gear 111 from a rotational center of the magnet 115 by play between the holding hole 123 and the magnet 115.
Further, in integrating the magnet 115, a drawback of chipping the magnet 115 is liable to bring about since the temporarily opened press claw member 127 is strongly brought back to impinge on the magnet 115.